This invention relates to aircraft ground proximity warning systems and more particularly to ground proximity warning systems that utilize speed versus altitude relationships to generate warning signals indicating unsafe flight profiles.
In the prior art warning systems, as represented by Astengo U.S. Pat. No. 3,715,718 and the applications of Bateman Ser. No. 480,727 and a subsequent application by Bateman entitled "Aircraft Landing Approach Ground Proximity Warning System," Ser. No. 511,757 filed on Oct. 3, 1974 all assigned to the assignee of the present invention, there is no direct relationship between the speed of aircraft and the altitude at which a warning is generated. In the application of Bateman entitled "Aircraft Ground Proximity Warning System with Speed Compensation," Ser. No. 511,674 filed on Oct. 3, 1974 also assigned to same assignee as this invention, an apparatus is disclosed for increasing the warning time as a function of the aircraft speed. However, this system utilizes the rate of change of the aircraft's altitude and does not make use of a measure of the aircraft's actual altitude above ground as a primary criteria for providing a warning.
Normally, an aircraft proceeding at a relatively high rate of speed is considered not to require a terrain warning system since it is assumed that the aircraft is at a normal operating altitude where the chances of impacting the terrain are fairly remote. However, there are a number of circumstances where this assumption may not hold true, such as an aircraft assuming an incorrect attitude through pilot error, e.g. flying toward the ground when it should be in level flight or climbing. Another example may occur where an aircraft is flying through mountainous territory or is beginning a landing approach to an airfield that is surrounded by high hills or mountains. While it is considered desirable to provide the crew of aircraft with warnings of the close proximity of the ground during relatively high speed operation, at the same time, it is important to keep the number of nuisance warnings at a minimum. A nuisance warning is defined as a warning that is generated when the crew of aircraft is aware of all relevant factors and is ordinarly not obligated to take special action to avoid impacting the terrain. It is therefore important that a warning system discriminate, insofar as possible, between conditions indicating unsafe flight and normal flight conditions.